The subject matter described herein relates generally to wind turbines and, more particularly, to an electric power transmission system for a wind turbine in a geographically-isolated wind turbine farm and black start capabilities thereof.
Generally, a wind turbine includes a rotor that includes a rotatable hub assembly having multiple blades. The blades transform wind energy into a mechanical rotational torque that drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electric energy. Gearless direct drive wind turbines also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on a base that includes a truss or tubular tower. The generated electric power is transmitted to an electric grid via at least one electrical connection. Such known wind turbines are typically coupled to the electric grid via a known full power conversion assembly. Such known full power conversion assemblies include a rectifier portion that converts alternating current (AC) generated by the generator to direct current (DC) and an inverter that converts the DC to AC of a predetermined frequency and voltage amplitude.
At least some of the known wind turbines are physically positioned in a remote geographical region or in an area where physical access is difficult, such as, off-shore installations. These wind turbines may be physically nested together in a common geographical region to form a wind turbine farm and are electrically coupled to a common AC collector system. Many of these known wind turbine farms include a separated full power conversion assembly electrically coupled to the AC collector system. The rectifier portion of the separated full power conversion assembly is positioned in close vicinity of the associated wind turbines and the inverter portion of the separated full power conversion assembly is positioned in a remote facility, such as a land-based facility. Such rectifier and inverter portions are typically electrically connected via submerged high voltage direct current (HVDC) electric power cables.
Known wind turbines include support equipment that facilitates operation of such wind turbines, for example, blade pitch drive motors and lubrication pump motors. Moreover, such equipment is typically positioned in the nacelle or the tower. Further, many known wind turbines include auxiliary power equipment that receives at least a portion of electric power generated by the generators in the wind turbine farm to facilitate electrically powering such support equipment via the AC collector system. A single wind turbine generator in the wind turbine farm typically has sufficient electric power generation capacity to power the equipment for the remaining wind turbines that are removed from service.
In the event that all of the wind turbine generators in the remote farm are removed from service, an alternative method of transmitting electric power to the auxiliary power equipment and the associated wind turbine support equipment must be used to facilitate a restart of at least one wind turbine generator, i.e., to perform a black start of the wind farm. One such method is providing additional equipment, for example, a diesel-powered generator, locally positioned in the vicinity of the tower or within the tower. Another such method may include independent electric power transmission equipment, portions of which may need to be positioned within the tower and/or a land-based facility, those portions coupled via independent electric cables. Such additional equipment requires increased capital construction costs and increased operational maintenance costs of the remote wind turbine farm.